1. Technical Field
The present invention relates to an image display device and a method of controlling the image display device and, more specifically, a technology of the image display device that displays an image by scanning with a laser beam.
2. Related Art
In recent years, a laser projector employing a laser beam is proposed as an image display device for displaying images. The laser beam, which is a light beam, is characterized by high monochromaticity and directivity. Therefore, the laser projector has an advantage in that an image with high color reproducibility can be obtained. A high-output laser source is used in order to display an image by causing the laser beam to scan. The laser projector achieves display by scanning with a laser beam from the laser source at a high-speed and dispersing the same on the screen. By sealing the laser source in an enclosure, only the laser beam with dispersed intensity can be supplied out from the enclosure. Therefore, the laser beam of intensity higher than a predetermined intensity, which is considered to be dangerous, can be prevented from being emitted out of the enclosure while displaying a bright image. For example, when part of the screen is damaged, there is a case in which a laser beam which is insufficiently diffused in the screen is emitted out from the enclosure. Therefore, a technology to prevent a condition such that a laser beam of high intensity is emitted out from the enclosure from occurring by adapting the device to discontinue oscillation of a laser beam when damage of the screen is sensed. (for example, JP-A-2002-281532, JP-A-2002-372752 and JP-A-2004-341210.
As means that senses damage of the screen, an arrangement in which sensors arranged over the entire screen are used as in JP-A-2002-281532 and JP-A-2002-372752, or an arrangement in which an image-pickup device or the like that monitors a state of the screen as a technology disclosed in JP-A-2004-341210 are considered. The arrangement in which the sensors arranged over the entire screen are used is advantageous in that detection of minute damage on the entire screen is ensured. On the other hand, since a number of sensors are necessary for detecting damage on the entire screen, a cost is increased. In addition, since the amount of light which is not used for forming the image is increased, and hence the efficiency of light utilization is lowered. The arrangement in which the screen is monitored by the image-pickup device or the like is advantageous in that one single sensor is sufficient. However, since a sensor of high resolution is necessary for ensuring detection of minute damage, increase in cost is resulted. As described above, according to the related art, a problem such that it is difficult to detect abnormality of the screen with an arrangement which is simple and is able to reduce lowering of the efficiency of light utilization.